Hello Nabhya,
Thank you for reaching out to the Microsoft Community and I'll be glad to assist you today.
If your device does not go into the Sleep or Hibernate mode when selecting Power > Sleep, please check the following settings.
1. Check Power Plan settings.
a. Type "Choose a Power Plan" in the search bar on the taskbar and click enter.
b. Select choose what power buttons do on the left pane.
c. Select When I press the Power Button and Sleep Button all to Sleep.
d. Click Save changes.
2. Turn Off Fast Startup.
a. Type "Choose a Power Plan" in the search bar on the taskbar and click enter.
b. Select choose what power buttons do on the left pane.
c. Click Change settings that are currently unavailable.
d. Uncheck "Turn on Fast startup check box" and click Save changes.
3. Update BIOS.
a. Go to your PC manufacturer's website.
b. Enter your computer model number.
c. See if you have the latest BIOS updates available for your device.
d. Download and install them.
4. Disconnect external peripherals.
External devices such as Monitors, external hard drives, printers, CDs, keyboards, or mice can sometimes prevent your device from entering sleep mode. Just disconnect them to see if the device normally enters into sleep mode.
5. Disable or check the Background apps.
Sometimes third-party apps or drivers might run in the background preventing the device from entering into sleep mode. Open the task manager and disable all the startup apps and some background apps which might be the reason for the issue.
You can check which app or driver is waking your PC when entering into sleep mode. Run the code in the command Prompt Window.
powercfg /lastwake
I hope this information helps. If you have any questions, please let me know and I will be happy to help you further.
Best regards,
Gunasekar N
